KIEV — With their country caught in a fierce tug-of-war between Russia and the West over a new security order, Ukrainians elected Petro O. Poroshenko as president Sunday, turning to a pro-European billionaire to lead them out of six months of wrenching turmoil, including a continuing separatist insurrection in the east.
The special election was called by Parliament to replace Viktor Yanukovych, who fled Kiev on Feb. 21 after a failed but bloody attempt to suppress a civic uprising, and whose toppling as president set off Russia’s invasion and annexation of Crimea.
The election allows Ukraine to open a new chapter in its history, and even President Vladimir Putin of Russia has indicated in recent days that he would accept the result.
But Poroshenko faces the excruciatingly difficult task of trying to calm and reunite a country that has been on the edge of financial collapse and on the verge of tilting into civil war. Among his chief tasks will be to ease tensions with Russia.
“Now we have a state of war,” he said as he arrived at a polling station in Kiev to vote Sunday. “We need to establish peace.”
Early exit poll results showed Poroshenko — a confections tycoon known as the Chocolate King, and a longtime veteran of Ukrainian politics — with a wide lead over his strongest rival, the former prime minister Yulia V. Tymoshenko. He appeared poised to easily clear the simple-majority threshold needed to avoid a potentially divisive runoff.
The polls, conducted by three respected Ukrainian survey agencies, found the 48-year-old Poroshenko getting 55.9 percent of the vote in the field of 21 candidates, the Associated Press reported. Tymoshenko was a distant second, with 12.9 percent. Full results are expected Monday.
Fewer than 20 percent of the polling stations were open in the east after gunmen smashed ballot boxes, shutting down polling centers, and issued threats. Nationwide, about 60 percent of 35.5 million eligible voters turned out, the central elections commission said.
Poroshenko declared victory at an evening news conference at an arts center, where he appeared with the former champion boxer Vitali Klitschko, a leader of the street protests that deposed Yanukovych. Klitschko was elected Sunday as mayor of Kiev, the capital. The arts complex was decked out for a victory party, including cases of Spanish and Italian wine.
“These were the hardest periods in Ukraine’s history, and these elections determine the future of our country,” Poroshenko said. “I would like to thank the Ukrainian people who participated and showed record support, and visited all polling stations in these hard conditions.”
Despite formidable obstacles in the east, international observers predicted that the presidential vote would receive high marks in meeting standards of fairness.
But Poroshenko faces skepticism even among many of his supporters, who are wary both of his status as a billionaire businessman and because he is a veteran in Ukraine’s notoriously corrupt politics.
He has been a longtime member of Parliament, where he briefly served as speaker, and was minister of trade and economic development under Yanukovych and foreign minister under former president Viktor Yushchenko.
Poroshenko has vowed repeatedly to set Ukraine on a pro-European course, and he has pledged to sign the political and trade agreements with the European Union that Yanukovych abandoned, setting off the uprising last fall.
But Poroshenko has deep business interests in Russia and has previously served in pro-Russia governments, creating some optimism in Moscow that negotiations are possible. The Kremlin has already seized a factory and warehouse in Lepetsk, Russia, belonging to Poroshenko’s company, Roshen Chocolate.
Last year, in the run-up to tensions over the European Union agreements, Russia also barred imports of his chocolate, citing vague health concerns.
Poroshenko has repeatedly called for armed separatists to be brought to justice, but he also ran a campaign focused on the bread-and-butter issues of jobs and the economy, as well as a populist anticorruption message that resonated well with an electorate weary after more than two decades of malfeasance and mismanagement.
Ukraine will be under continuing pressure from Russia, which is demanding billions of dollars for unpaid natural-gas bills, and has made clear that it could cripple the Ukrainian economy at any moment with trade sanctions.
There is also pressure from the International Monetary Fund, which has laid out strict requirements, including austerity measures, in exchange for $27 billion in emergency credit that saved the country from default.
The crisis in Ukraine began six months ago when Yanukovych broke a promise to sign political and economic accords with the European Union. A confrontation between Russia and the West followed, including military maneuvering, economic sanctions, and travel restrictions.
The interim government, led by Prime Minister Arseniy P. Yatsenyuk, has already taken steps toward finalizing the agreements that Yanukovych abandoned.
Sunday’s vote had the broad support of leaders in Europe and the United States. In St. Petersburg, Putin, too, expressed support Saturday. “We will respect any choice made by the Ukrainian people,” he said at a round-table interview with international news agencies.